Defoamers are compositions used in the pulp and paper mill industry for the control of foam in various processes. For instance, a defoamer is useful in Kraft pulp stock, sulfite stock, screen room, bleach plant area and the like.
Prior art defoamer compositions are generally composed of a carrier fluid, a defoaming agent and miscellaneous additives. The most cost effective carrier fluids of the prior art have been the petroleum oils (mineral oils) because of their low cost and abundance. Water has been favored also as an extender of the anhydrous defoamers, when necessary to lower the product cost. Various defoaming compositions have been documented in product literature and patents. See, e.g., U.S. Pat. Nos. 5,082,590; 5,096,617 and 5,071,591.
An example of a conventional defoamer is called Brown Stock Wash (BSW) Defoamer. The key components for BSW defoamer compositions are mineral oil (petroleum oil), hydrophobic silica, ethylene-bis-stearamide (EBS) and silicone oil. In all publications and commercial formulas of the BSW defoamers, EBS has been one of the essential components, because it is the most cost effective defoaming agent known to the pulp and paper industries. Various mixtures of the above ingredients have been in use along with some special additives in current commercial defoamers, which are economically successful.
Pulp and paper industries have been troubled in the past several years by potential discharge of undesirable by-products, such as the carcinogenic dioxins, from their chemical (bleaching) process. The petroleum oils used in defoamers have been confirmed to contain dioxin precursors (dibenzodioxin and dibenzofuran) which are converted to dioxins during the bleaching process in the mills. Thus, all defoamer suppliers have been working on suitable replacements for the petroleum oils because of worldwide concern about the health hazards and environmental problems linked to the petroleum oils. The mineral oils are no longer favored by many responsible pulp and paper mills.
Another major problem facing pulp and paper mills has been the EBS. The EBS-containing defoamers have been the most cost effective products for the past 30 or more years. The EBS has been the champion component for the pulp defoamer development and far superior even to silicone oil on a cost basis. However, the EBS in the pulp and paper mill processes has the detrimental side effect of producing unwanted deposits. The hardest deposit is caused by the EBS, which has a high melting point and low solubility. All pulp and papers mills, along with defoamer suppliers, have been searching for an EBS replacement which will not sacrifice defoamer performance. See, e.g., the defoamer composition described in U.S. Pat. No. 5,152,925.
Present pulp and paper mills depend even today upon the EBS and petroleum components in many formulations. These two components are the necessary evils that the pulp and paper mills have often been forced to use because of their cost effectiveness.
There remains a need in the paper and pulp processing industries for cost effective and functional defoamer compositions which do not have the disadvantages caused by the presence of petroleum and EBS.